The present invention relates in general to a spinning process which is one of plastic working processes and more specifically to a method of forming an integral tubular projection which is shaped like a boss, in a disk-shaped work by spinning.
An example of this kind of plastic working or spinning process is disclosed in Japanese Patent Provisional Publication No. 9-506295.
The prior art spinning process is adapted to form a boss of a part by collecting a material of a work around a pin gradually by shear spinning and pushing it into a space defined by an upper surface of a lower jig, a lower surface of an upper pressure jig and an outer circumferential surface of the pin integral with the lower die, namely, materially by the full closed die forging technique. Accordingly, the inner and outer diameters of the boss of the formed part are determined depending upon the diameter of the pin.
A problem of the prior art spinning process is that unless the lower jig is replaced by one having a pin of a different size, a part having a boss of a different inner diameter cannot be produced. Another problem is that it is necessary that a work is previously formed with a hole into which the above described pin is to be inserted. The problems inevitably increase the number of necessary process steps and therefore the manufacturing cost.
It is accordingly an object of the present invention to provide a spinning process which can form a hollow cylindrical projection or boss of a desired inner diameter in a work with ease and without being restricted by the size of the above described pin and without requiring a prepared hole in the work.
To accomplish the object, there is provided according to an aspect of the present invention a method of forming an integral tubular projection in a disk-shaped work, the work having a flat plate portion, the method comprising: driving the work to rotate in such a manner that the flat plate portion is held positioned on a plane; spinning the work by using a forming roller whose axis is inclined to form a predetermined angle with an axis of rotation of the work, in such a manner as to cause a section of the work to decrease in thickness and another section of the work to increase in thickness and grow to the tubular projection;
wherein:
h=0.1 to 0.5t;
d=0.25 to 0.94D;
T=0.5 to 7h;
V=0.029 to 0.234xcfx80D2h;
where h is a depth by which the forming roller cuts into the work, t is a thickness of the work, d is an outer diameter of the tubular projection, D is a diameter of a circle including a point where the spinning by the forming roller starts, T is a thickness of a wall of the tubular projection, and V is a volume of the tubular projection.
According to another aspect of the present invention, there is provided a method of forming an integral tubular projection in a disk-shaped work by spinning, comprising: forming the work into a shallow dish shape, the shallow dish-shaped work having an inclined wall portion other than a flat central portion where the projection is to be formed; supporting the shallow dish-shaped work on a mandrel shaped correspondingly to the shallow dish-shaped work; rotating the shallow dish-shaped work about an axis thereof together with the mandrel; pushing a forming roller against the inclined wall portion of the work while moving the roller along the inclined wall portion of the work and thereby causing the inclined wall portion to partially decrease in thickness and the central portion to partially increase in thickness and grow to the tubular projection.
According to a further aspect of the present invention, there is provided a method of forming a disk-shaped part having an integral, concentric boss in the form of a hollow cylindrical projection, by spinning, comprising: preparing a work in the form of a flat circular plate; holding the work between a mandrel and a tail stock and driving the work to rotate; pushing a forming roller against the work and thereby causing a radially outer section of the work to decrease in thickness and a radially inner section of the work to increase in thickness and grow to the boss while holding an inner circumferential surface of the projection apart from an outer circumferential surface of the tail stock.
According to a further aspect of the present invention, there is provided a product which is produced by either of the above described methods of the present invention.